Offshore structures such as a tension leg platform have long been used in different enterprises including oil and gas research platforms. There is typically a need to secure the platform to the sea floor. One method developed for this purpose is the keyhole latch anchor design which can be used at both the lower (sea floor) or upper (platform) ends of a tension leg platform tether system.
The keyhole latch design at the lower end of the tether system incorporates a receptacle anchored to the sea floor and a flex joint and latch assembly. The flex joint and latch assembly is attached to a tension member which extends upward to the floating offshore structure. The tension member is attached to the floating structure by a similar upper keyhole latch design. By inserting the flex joint and latch assemblies into the associated receptacles and then applying a suitable tension to the tension member, the floating offshore structure is secured in place.
Several disadvantages exist in the present design. Due to the currently designed keyhole latch geometry, some rolling of the back flange of the flex joint and latch assembly load ring on the receptacle will occur under load. This creates very high stresses and fretting on the back flange and load ring. Also, since the load ring must be segmented, i.e., a noncontinuous surface, to allow insertion of the flex joint and latch assembly, these stresses tend to force the load ring apart at the keyhole slot. If enough stress is applied, the anchor can be destroyed and will allow the flex joint and latch assembly to break free of the receptacle.